Articles such as pipes and tennis rackets, have been damped in the past by a variety of dampers. Examples of such dampers include the following.
U.S. Pat. No. 5,374,057 to Lai et al. describes the use of constrained layer dampers on a tennis racket frame to reduce the level of vibration transmitted from the frame to the player's hand. Two separate constrained layer dampers are applied either on the outer surface or on the inner surface of the frame and have shown improvement in reducing vibration level.
U.S. Pat. No. 5,294,119 to Vincent et al. describes particular applications of constrained layer dampers on a golf shaft. The first damper embodiment is a constrained layer damper which encircles the outside surface of a golf shaft. The second embodiment includes several constraining layers attached to the outer surface of the golf shaft by a continuous damping layer. In other words, the ring-shaped damping layer in one embodiment is used to attach the constraining layer to the golf shaft surface. The damping layer referred to in this patent is exposed to the environment on the outside of the shaft.
U.S. Pat. No. 5,087,491 to Barrett discloses a damped tube. The damped tube is essentially a three-layer structure with a damping layer between two layers of advanced fiber reinforced composite materials. The stiffness of the tube is controlled by the two composite layers. The total damping is optimized by tuning the anisotropic properties of fibers in such a way to transfer the strain into the damping layer for the purpose of generating shear strain.
U.S. Pat. No. 5,030,490 to Bronowicki et al. describes the use of ring-shaped dampers on both the inner and outer surface of a tube. The dampers are segmentedly placed along the axis of a tube. This placement of segmented dampers along tube axis could be effective when the vibration occurs along the tube axis.
U.S. Pat. No. 5,507,477 to Manning et al. discloses a tubular composite structure having multiple viscoelastic damping layers and stiff segmented constraining layers formed on the outside of a tubular layer of soft elastic material. This multilayer damping treatment is said to provide a way to improve structural damping over a wider range of temperature.
Patents for noise attenuation using acoustical absorbing materials include U.S. Pat. No. 4,435,877 to Berfield which discloses a noise muffler for a vacuum cleaner constructed of flexible open cell foam inserts and U.S. Pat. No. 5,418,339 to Bowen et al. which discloses a sound muffler for a pneumatic tool constructed of a nonwoven web of fibers coated with a binder resin.
Pieces of foam have been inserted in golf club shafts and have demonstrated improvement in structural borne sound. This demonstration occurred at the DISCON Conference in San Jose, Calif., in September of 1995.